Moderate paced cardio, done immediately after weight training, with a heart rate of 120-130 is suppose to burn more fat than higher intensity cardio and also help preserve muscle mass. I do incline walking or step mill at about this rate and have gotten great results doing 45 minutes per session, 5 days per week. Doing slower cardio might not seem like its doing much because your not gonna sweat or fatigue like you do when your doing high intensity, but it is suppose to tap into fat stores more effectively, and I cant disagree at this point, I'm leaner than I have ever been and I have been able to hold onto most of what I gained when I bulked over the winter.